1. FIELD OF INVENTION
This invention relates generally to the field of tensile testing of filaments and, more particularly, to a method and apparatus for testing microfilaments. Fibers as small as 0.001 inches in diameter and 0.040 inches in length have been tested, although the method and apparatus of the invention are capable of testing fibers of smaller diameter and length.
2. DESCRIPTION OF THE RELATED ART
Fibrous materials are used in a variety of applications both to provide reinforcement in composite matrices and as conduits in electronic components. In recent years, many new fibrous materials have been developed which are manufactured from both natural and synthetic components. Types of fibers used, for example, to reinforce plastic include glass, ceramic and polymeric fibers such as aramids. Useful fibers are available in a wide range of lengths and diameters suited to various applications and manufacturing techniques. In addition to size, the durability of fibers and their ability to withstand mechanical forces such as bending or pulling are determining factors with regard to their potential uses.
Tensile strength is one characteristic which is commonly tested in assessing suitability of fibers for particular applications. There are a number of instances in the prior art of methods and apparatuses for testing the tensile strength of fibers. Special fixtures are commercially available to test wire, rope and cable which generally include a gripping arrangement involving wrapping the specimen around a mandrel or capstan to avoid crimping or kinking the material which could affect the results of tests. This assumes that the sample is long and flexible enough to be successfully wrapped around a mandrel.
The ability to test small fibers is becoming increasingly important as scientists and engineers begin to model the complex mechanical properties of fiber-reinforced, composite materials. Tensile testing of microfilament specimens is, however, difficult and tedious since small. diameter, delicate specimens require special handling techniques. Although considerable effort has been expended in the past to develop test methods and equipment to facilitate the testing of fine, small diameter specimens (see, for example, W. F. Knoff, U.S. Pat. No. 4,909,084; J. E. Hargraves, U.S. Pat. No. 3,667,288, and C. E. Shulze, U.S. Pat. No. 3,602,040), problems of alignment, gripping and control still present significant challenges, especially for fibers of short length. To date, a satisfactory microfilament tensile testing system has not been developed which is capable of testing short, small diameter samples (on the order of 0.04 in. length.times.0.001 in. diameter).